The present disclosure relates to a spread spectrum clock generator, and, more particularly, relates to generation of a spread spectrum clock by using, for example, a delta-sigma modulator.
A spread spectrum clock generator (SSCG) is used to prevent occurrence of an EMI (Electro-Magnetic Interference) caused by an electronic device. The SSCG generates a spread spectrum clock signal by modulating, according to a predetermined modulation frequency and the degree of modulation, the frequency of a clock signal which is generated by a PLL (phase locked loop) or the like.
The SSCG disclosed in Japanese Unexamined Patent Application Publication No. 2010-035015 cyclically increases or decreases a phase difference between a feedback clock signal and a reference clock signal to be inputted to a phase comparing unit, by causing a phase interpolator disposed on a feedback path to advance or delay the phase of an output clock signal of a voltage-controlled oscillator, and modulates the frequency of the output clock signal.
Further, there is an SSCG which causes a delta-sigma modulator to delta-sigma modulate a waveform signal for controlling spreading of the spectrum of an output clock, and modulates the frequency of the output clock based on a resulting compressional wave.